void main(List<String> args) {

  //1.if语句
  int score = 80;
  if (score >= 90) {
    print('A');
  } else if (score >= 80) {
    print('B');
  } else if (score >= 70) {
    print('C');
  } else if (score >= 60) {
    print('D');
  } else {
    print('E');
  }
  //2.if语句的省略形式
  if (score >= 60) {
    print('及格');
  }
  //3.if语句的嵌套
  if (score >= 60) {
    print('及格');
    if (score >= 70) {
      print('中等');
    }
  }

  int score2=699;

  score2>=700?print('成绩超出范围'):print('成绩正常');


  int orderState=3;
  switch(orderState){
    case 1:
      print('待付款');
      break;
    case 2:
      print('待发货');
      break;
    case 3:
      print('待收货');
      break;
    case 4:
      print('待评价');
      break;
    case 5:
      print('已完成');
      break;
    default:
      print('未知状态');
  }
  //4.while循环
  int i=0;
  while(i<10){
    print(i);
    i++;
  }
  //5.do...while循环
  do{
    print(i);
    i++;
  }while(i<10);
  //6.for循环
  for(int j=0;j<10;j++){
    print(j);
  }
  //7.break和continue
  for(int k=0;k<10;k++){
    if(k==5){
      break;
    }
    print(k);
  }
  for(int l=0;l<10;l++){
    if(l==5){
      continue;
    }
    print(l);
  }
  //8.循环嵌套
  for(int m=0;m<10;m++){
    for(int n=0;n<10;n++){
      print('$m-$n');
    }
  }

}